Refining Scale Measurement: Reassessing Oral Impacts on Daily Performances Properties With Item Response Theory

Many oral health-related quality of life instruments have been developed but few have undergone a comprehensive psychometric assessment. One commonly used measure is the Oral Impact on Daily Performance (OIDP). This study revised the configural and metric properties as well as the performance of items based on Item Response Theory (IRT) of a dichotomous-item version of OIDP in Brazil.

The nine-item dichotomous version of the OIDP was analysed using data from a nationally representative sample from the Oral Health Survey (SBBrasil 2010). It consisted of 30 064 individuals aged 12 to 75 and was split into two partitions comprising n₁ = 20 040 and n₂ = 10 024, respectively. Confirmatory factor analyses (CFA) were conducted on the larger partition and cross-validated on the smaller to assess configural and metric properties. The item performance was evaluated using a 2-parameter item response theory (IRT) model. Sampling weights were used in all analyses.

The unidimensional model presented two violations of conditional independence, one between items i5 (practising sports) and i4 (going out) and another between items i6 (trouble in speaking) and i7 (shame of speaking or smiling). A CFA of the most parsimonious model (removing i5, i6 and i7) yielded a RMSEA = 0.02, WRMR = 1.42, CFI = 0.99 and TLI = 0.99. The IRT analyses showed that three pairs of items had very similar levels of difficulty and discrimination suggesting redundancy.

A shorter dichotomous version of the OIDP scale has acceptable configural and metric properties. Being more concise and thus efficient, it may be better suited for large-scale population surveys than the version currently in use.